Covers a test method for the determination of the residual resistance ratio (RRR) of Nb3Sn composite conductors. This method is intended for use with superconductor specimens that have a monolithic structure with a rectangular or round cross section, RRR less than 350 and cross-sectional area less than 3 mm2, and have received a reaction heat-treatment. Ideally, it is intended that the specimens are as straight as possible; however, this is not always the case, thus care must be taken to measure the specimen in its as received condition. All measurements are done without an applied magnetic field.The method described in the body of this standard is the "reference" method; optional acquisition methods are outlined in Annex A.